The morphometric and cephalometric study of anterior cranial landmarks for surgery.

OBJECTIVE: The aim of this work was to determine reliable bony landmarks for the anterior skull base and to standardize some specific dimensions among the frontal sinus and neighboring structures for safe anterior cranial surgery. METHODS: The study consisted of a topographical anatomic examination and cephalometric analysis of the skull. Thirty adult skulls (60 sides) were studied regarding the localization and dimensions of the supraorbital foramen (SOF), frontal sinus (FS), frontozygomatic fissure, infraorbital foramen, anterior nasal spine, and nasion. Differences between the measurement of skulls and cephalograms were analyzed by Student's t test. The Pearson correlation test was used for statistical analysis of the cephalogram. RESULTS: Examination of the 60 sides of the bony heads revealed that the shape of the SOF was a foramen in 25 sides (41%), a notch in 29 sides (49%), and a groove in 6 sides (10%). A total of 20 (33%) SOFs were inside the FS and the mean distance was 6.3+1.34 mm from the lateral border of the sinus, 27 (45%) of SOFs were outside of the FS and the mean distance was 8.8+2.01 mm, and 13 (22%) of SOFs were at the border of the FS. According to our measurements the medial border of the craniotomy should be placed approximately 43 mm lateral to the nasion to avoid entering into the frontal sinus. CONCLUSION: To plan and to decide the convenient and safe anterior midline skull base approach and to avoid postoperative complications, bony landmarks and anatomic measurements around the SOF and FS will be helpful for the surgeon to constitute a simplification of topographic anatomy.     

向鞍上、鞍旁扩展的经蝶窦手术入路相关结构的显微解剖研究

目的为扩大经蝶窦手术提供蝶窦外侧壁和海绵窦内侧面观、蝶骨平台骨窗腹面观以及蝶窦后方斜坡周围的显微解剖参数。方法20具干颅骨漂白标本(40侧)用于观察入路相关的骨性解剖结构;15具成人头颅灌注标本(30侧)模拟扩大经蝶窦入路,研究垂体周边解剖结构的位置关系,测量相应的距离或手术相关角度。同时,利用血管铸型技术,对鞍周静脉窦及动脉分支进行形态学观察。结果后组筛窦形成蝶旁、蝶上筛房,对扩大经蝶窦入路术中视野显露有直接影响。视神经管颅口内侧缘间距为(15.7±3.2)mm,鞍结节处颈内动脉间距为(13.9±3.8)mm,鞍结节后缘与筛板后缘之间的距离平均为(23.3±3.2)mm,视神经管与矢状面夹角为36.3°±1.6°。提示扩大经蝶窦手术入路相关的骨窗为“”型。结论扩大经蝶窦入路向鞍旁、鞍前、蝶骨平台扩展适合沿中线生长的的中、小型病灶。向鞍旁海绵窦扩展时,垂体与海绵窦段颈内动脉关系密切,增加施行扩大经蝶手术的风险。术中最易损伤的是颈内动脉和外展神经。     

Extended middle fossa approach: quantitative analysis of petroclival exposure and surgical freedom as a function of successive temporal bone removal by using frameless stereotaxy

OBJECT: Conventional wisdom regarding skull base surgery says that more extensive bone removal equals greater exposure. Few researchers have quantitatively examined this assertion, however. In this study the authors used a frameless stereotactic system to measure quantitatively the area of petroclival exposure and surgical freedom for manipulation of instruments with successive steps of temporal bone removal. METHODS: With the aid of high-power magnification and a high-speed drill, 12 cadaveric specimens were dissected in four predetermined, successive bone removal steps: 1) removal of the Kawase triangle; 2) removal of the Glasscock triangle; 3) removal of the cochlea together with skeletonization of the anterior internal auditory canal; and 4) inferior displacement of the zygoma. Step 1 offered 62 +/- 43 mm2 of exposed petroclival area, with 84 +/- 69 mm2 of surgical freedom; Step 2, 61 +/- 22 and 76 +/- 58 mm2; Step 3, 128 +/- 47 and 109 +/- 87 mm2; and Step 4, 135 +/- 38 and 102 +/- 69 mm2, respectively. CONCLUSIONS: The middle fossa approach provided a means surgically to expose the petroclival area. When examined quantitatively by using a frameless stereotactic device, the authors determined that the removal of the cochlea and skeletonization of the anterior internal auditory canal (Step 3) provided the most significant increase in both exposure and surgical freedom. Removal of the zygoma improved neither exposure nor surgical freedom.     

Posterior condylar canals and posterior condylar emissary veins—a microsurgical and CT anatomical study

The posterior condylar canals (PCCs) and posterior condylar emissary veins (PCEVs) are potential anatomical landmarks for surgical approaches through the lateral foramen magnum. We conducted computed tomography (CT) and microsurgical investigation of how PCCs and PCEVs can aid in planning and performing these approaches. We analyzed the microanatomy of PCCs and PCEVs using cadaveric specimens, dry skulls, and CT images. The recognition frequency and geometry of PCCs and PCEVs and their relationships with surrounding structures were evaluated. PCCs were identified in 36 of 50 sides in dry bones and 82 of 100 sides by CT. PCCs had a 3.5-mm mean diameter and a 6.8-mm mean canal length. We classified their courses into four types according to intracranial openings: the sigmoid sinus (SS) type, the jugular bulb (JB) type, the occipital sinus type, and the anterior condylar emissary vein type. In most cases, PCEV originated near the boundary between the SS and JB. PCCs and PCEVs can be useful anatomical landmarks to differentiate the transcondylar fossa approach from the transcondylar approach, thus preventing unnecessary injury of the atlantooccipital joint. They can also be used as landmarks when the jugular foramen (JF) and hypoglossal canal (HGC) are being exposed. The area anterior to the brain stem and the medial part of HGC can be accessed by removal of the lateral foramen magnum medial to PCC. JF and the lateral part of HGC can be accessed by removal of the skull base lateral to PCC without damaging the lateral rim of the foramen magnum.     

Anatomo-radiological evaluation of lateral approaches to the skull base

Our objective is to correlate the anatomical exposure provided by complex skull base approaches to the lateral skull base with their CT and MRI scans counterparts and to introduce a modular concept emphasizing the derivation of complex skull base approaches from simpler ones.We executed 10 lateral approaches to the skull base in 20 embalmed cadaveric heads (40 sides). Each approach was executed a minimum of three times on each specimen. These approaches were the pterional and its modifications, the subtemporal and its modifications, and the suboccipital and its modifications. We correlated the approaches and the areas of the skull base exposed by scanning the surgical cavity filled with material imageable by CT and MRI and throughly surveying the operative field.Visualization of the area of the skull base exposed was excellent using our CT-MRI imageable cadaveric preparation. The topographic areas of the skull base exposed correlated well with their radiological counterparts.The areas of the skull base exposed by each of the complex surgical approaches to the skull base were clearly delineated by using our anatomo-radiological correlation. Complex approaches to the skull base are formed by simple neurosurgical approaches (building blocks) to which different modules are added.     

Endoscopic endonasal skull base surgery: Part 1--The midline anterior fossa skull base.

OBJECTIVE: An endonasal endoscopic surgery to the anterior fossa skull base was developed in cadaver dissection as a minimally invasive surgical technique and, subsequently, used in patient treatment. METHODS: Six cadaver head specimens were used. Ideal head positioning and various surgical routes were studied. To estimate the extent of surgical exposure provided by this technique, the width of the exposed anterior cranial fossa was measured between the medial margin of the orbits, the optic nerves and the carotid arteries. Three demonstrative patient cases are presented. RESULTS: Ideal head positioning was discovered to be at 15-degree extension of the forehead-chin line. Paraseptal, middle meatal and middle turbinectomy approaches were developed. The average width between the medial orbits was measured to be 24 mm (range 22-29 mm) at the crista galli level, 27 mm (range 24-30 mm) at the planum sphenoidale, 18 mm (range 15-22 mm) between the optic nerves, and 17 mm (range 13-21 mm) between the rostral carotid siphons. This technique, when it was applied in patient care, proved to be minimally invasive. CONCLUSIONS: This endoscopic endonasal approach provided a direct "short-cut" access to the midline anterior fossa skull base. This technique can be used for the surgical treatment of cerebrospinal fluid (CSF) leak, meningiomas, craniopharyngiomas, pituitary adenomas, and other midline intracranial anterior skull base lesions. This is the first report in the English literature describing endonasal endoscopy for the surgical treatment of primary intracranial anterior fossa skull base lesions.     

Quantitative analysis of the transcondylar approach to the foramen magnum

OBJECTIVE: Condylar resection with suboccipital craniotomy increases foramen magnum exposure, but guidelines for when this is necessary are not defined. Cadaveric and computed tomography evaluations were completed to guide decision-making regarding the use and extent of condylar resection. METHODS: Quantitative analysis of foramen magnum surgical exposures was performed on 32 skulls (64 sides) and 6 cadaveric dissections (12 sides). Computed tomographic (CT) scans were performed on cadaveric heads before and after condylar resections. Digitized images of dry skulls and CT images of cadaver heads were quantitatively analyzed. Predissection CT measurements of cadaveric heads guided extent of condylar resections, and resection accuracy was assessed with postdissection CT scans. RESULTS: Skull measurements (means in parentheses) included the foramen magnum area (7.8 cm(2)), length (3.6 cm), width (3.1 cm), anteroposterior condylar length (2.3 cm), and axial condylar length (2.5 cm). Mean widths of potential surgical exposures for skulls were obtained for A) suboccipital craniotomy (2.3 cm), B) with 25% (2.6 cm), and C) 50% condylar resection (3.0 cm). Mean angles of exposure were as follows: A, 38.4 degrees; B, 49.1 degrees; and C, 54.3 degrees. CT scans of cadaveric heads before and after dissections yielded measurements of exposure equivalent to measurements found on the dry skulls. CONCLUSION: On average, lateral exposure increases by 3 mm (13%) and 7 mm (30%) for 25 and 50% condylar resection, respectively, compared with suboccipital craniotomy alone. Angles of exposure increase by 10.7 degrees (28%) and 15.9 degrees (41%). Measurements of CT images can be used preoperatively to help analyze the need for condylar resection and intraoperatively to guide the extent of condylar resection.     

Olfaction preservation in anterior cranial base approaches: an anatomic study

OBJECTIVE: To study the anatomic basis for olfaction-sparing anterior cranial base approaches. METHODS: The medial anterior skull base containing the olfactory unit and delimited by the inner table of the frontal sinus, the lesser wing of the sphenoid bone, and the medial orbital walls was removed from six cadaveric specimens. Histological methods were used to investigate the location, distribution, and depth of penetration of olfactory nerves. Hematoxylin and eosin and Gomori trichrome staining were used to visualize landmarks and architecture. S-100 neurofilament protein immunostaining was used to identify nerve fascicles and axons. In three cadaveric head specimens, olfaction-sparing craniofacial approaches were performed and the excised olfactory units were evaluated histologically. RESULTS: Bundles of olfactory nerves were identified primarily in the nasal septum; relatively fewer bundles could be identified in the middle turbinate. Olfactory nerve endings were identified up to 20 mm below the cribriform plate (range, 7-20 mm). The superior and middle nasal meatus were most innervated; olfactory innervation was virtually absent in the inferior nasal meatus. Histological evaluation of the olfactory unit elevated during olfaction-sparing techniques routinely revealed transection of olfactory nerves that exited the skull base. CONCLUSION: In olfaction-sparing anterior cranial base approaches, the olfactory nerves are inevitably transected. The clinical significance of olfactory nerve transection for postoperative functional recovery of olfaction remains to be analyzed.     

颅颈结合区的显微外科解剖

目的：探讨颅颈结合区各结构的形态和毗邻关系,以提高颅内手术远外侧入路的安全性。方法：在手术显微镜下,对10个尸体头颅标本颅颈结合区进行显微解剖,对20个颅底枕骨大孔区进行观测,4个尸体头颅标本切制成0．5－1．0mm,超薄断层切片,观察颅颈结合区有关结构。结果：椎动脉第3段长21．6（15．3－31．9)mm,椎动脉沟呈浅沟者占80％,枕髁长为26．8（25．1－28．2)mm,前,后,中1／3部的厚度分别为9．9（9．6－10．6）,11．2（9．2－13．1）和8．6（8．3－9．0）mm,枕髁后极至舌下神经管颈内口距离为9．9（8．6－11．4）mm,至颅外口距离为16．1（13．5－17．1）mm,寰椎横突是重要的骨性标志,结论：掌握该区椎动脉的走行,枕髁的形态及毗邻关系,有助于预防远外侧入路至靶区时重要结构的损伤。     

A computed tomography scan and anatomical cadaveric study of the pterygopalatine ganglion for use in Gamma Knife treatment of cluster headache

OBJECT: Gamma Knife surgery has recently been used to treat patients with cluster headaches. Both the trigeminal nerve root and the pterygopalatine ganglion (PPG) have been targeted. However, there are no clear-cut anatomical landmarks on computed tomography (CT) scans or magnetic resonance images that accurately identify the PPG. Therefore, the authors performed microsurgical dissections on latex-injected cadaver heads to expose the PPG and correlated the findings with thin-slice axial CT scans obtained in the same heads to determine how best to target the PPG. METHODS: Three cadaver heads (five sides) previously injected with colored latex were dissected using skull base approaches and microsurgical techniques to identify the PPG and surrounding structures. Measurements were then made to different osseous anatomical landmarks such as the foramen rotundum, vidian canal, and so on. The PPG was marked with a radiopaque marker and thin-slice CT scans were obtained in the cadaver heads to develop some correlates that could be used to identify where the PPG is located on CT scans. RESULTS: The PPG was clearly identified in all specimens and had a mean diameter of 3.58 +/- 0.6 mm. The PPG was always located in the same plane (lateral and vertical) as the vidian canal and was located on average 2.7 +/- 0.3 mm from the end of the canal. The vidian canal was clearly identified on coronal CT scans and had a diameter of 3.05 mm. CONCLUSIONS: There was a clear and constant relationship between the PPG and vidian canal. The vidian canal is easily identified on coronal CT scans and can be used as a landmark to target the PPG with the Gamma Knife.     

Transtemporal approach to the skull base: an anatomical study

The surgical anatomy of a transtemporal approach to the structures of the clivus was defined with the aid of dissections in 10 cadaver heads. The steps in the dissection consisted of first exposing the cervical internal carotid artery (ICA), the internal jugular vein, and the caudal cranial nerves, each at the skull base; then performing small retromastoid and temporal craniotomies; and, finally, drilling away the petrous and tympanic bone to expose the intratemporal parts of the facial nerve, the petrous ICA, the sigmoid sinus, and the jugular bulb. To expose the structures of the lower clivus, the sigmoid sinus was ligated and divided, the facial nerve was displaced anterosuperiorly, and the inner ear structures were preserved. Dural opening exposed the anterolateral and anterior surfaces of the medulla, the pontomedullary junction, and the spinomedullary junction. The ipsilateral vertebral artery and often the contralateral vertebral artery and the vertebrobasilar junction, the caudal cranial nerves, and the origin of the 6th, 7th, and 8th cranial nerves were well exposed. To expose the structures of the middle clivus, we drilled away the labyrinth, the cochlea, and a portion of the clival bone. The facial nerve was displaced posteroinferiorly. Dural opening exposed the ipsilateral anterior surface of the pons, the midbasilar artery, and the ipsilateral 5th, 6th, 7th, and 8th cranial nerves. A portion of the contralateral anterior surface of the pons was also exposed at times. The superior limit of this exposure was just above the origin of the trigeminal nerve. The exposure of the upper clival structures was limited with this approach, and required medial temporal lobe retraction. Two case reports are included to illustrate the application of the transtemporal approach to the exposure and clipping of aneurysms of the vertebrobasilar system. The advantages and disadvantages of this approach are discussed.     

Radiographic Imaging of the Distal Dural Ring for Determining the Intradural or Extradural Location of Aneurysms

The effectiveness of several anatomical and radiological landmarks proposed to determine whether an aneurysm is located intradurally or extradurally is still debated. In anatomical and radiological studies, we examined the relationships of the distal dural ring (DDR) to the internal carotid artery (ICA) and surrounding bony structures to aid in the localization of aneurysms near the DDR. Anatomical relationships were examined by performing dissections on 10 specimens (5 formalin-fixed cadaveric heads). After the position of the DDR, optic nerve, and tuberculum sellae were marked with surgical steel wire, radiographs were taken in multiple projections. The only bony landmark consistently visible on radiographs was the planum sphenoidale. The superior border of the DDR is located at or below the level of the tuberculum sellae, which laterally becomes the superomedial aspect of the optic strut; thus, the optic strut marks the dorsal limit of the DDR. On 50 dry skulls, we measured the vertical distance between the planum sphenoidale and medial aspect of the optic strut (5.0 +/- 0.4 mm), the interoptic strut distance (14.4 +/- 1.4 mm), and the linear distance between the most posterior aspect of the planum sphenoidale (limbus sphenoidale) and the tuberculum sellae (6.0 +/- 0.5 mm). Using these measurements and the planum sphenoidale, tuberculum sellae, and optic strut as reference landmarks, we determined the location of the aneurysm relative to the DDR on angiographic images. In this way, we were able to identify whether lesions were intra- or extradural.     

Real-Time Imaging with the O-Arm for Skull Base Applications: A Cadaveric Feasibility Study

Introduction Although intraoperative imaging/navigation has established its critical role in neurosurgery, its role in cranial base surgery is currently limited. Due to issues such as poor bony resolution and accuracy, surgeons have to rely on anatomic landmarks that can be distorted by pathology when drilling out critical structures. Though originally developed for spinal application, we hypothesized that the O-Arm could address the above issues for use in cranial base procedures.Methods A cadaveric study was performed in which heads underwent a preprocedure scan via the O-Arm, a fluoroscopic device capable of providing three-dimensional images through the use of cone-beam technology. Preprocedure scans were taken and then registered to a Stealth S7 machine (Medtronic, Inc., Minneapolis, MN, USA). Key cranial base landmarks were identified on these scans and then subsequently identified under direct visualization after (1) endoscopic endonasal dissection and (2) a middle fossa approach. We then quantified the difference in distance between the preplanned and identified structure during surgery. This difference was considered the error.Results For anterior cranial fossa structures, the mean error was 0.25 mm (anterior septum), 0.27 mm (left septum), and 0.32 mm (right septum). For middle fossa structures, the errors were: 0.11 mm (foramen spinosum), 0.44 mm (foramen rotundum), and 0.21 mm (foramen ovale).Conclusion Based on this preliminary cadaveric study, we feel the O-Arm can provide the necessary imaging resolution at the skull base to be employed for intraoperative navigation during cranial base approaches (open and endoscopic). This study warrants further investigation into its clinical use in patients undergoing similar surgical procedures.     

Endoscope-assisted far-lateral transcondylar approach to the skull base.

The far-lateral transcondylar approach was used in this cadaveric study in an attempt to evaluate the usefulness of endoscope-assisted microsurgery in this region of the skull base. The study was carried out using 4 latex-injected, formalin-fixed cadaver heads. After initial examination of intradural structures under an operating microscope, a zero degree 4 mm diameter solid-rod endoscope lens was introduced and guided into position under the direction of the operating microscope. Photographs of the regional anatomy were taken through this lens and through a 30 degree angled lens and compared to photographs of the anatomy taken through the microscope. Clear close-up views of the dural portals and intradural course of the cranial nerves were obtained using the endoscope. The endoscope was introduced through three corridors enclosed with cranial nerves, providing the surgeon with panoramic views of the vertebrobasilar arteries and anterior brainstem surface. The endoscope can be guided through narrow corridors and placed immediately adjacent to a region of interest at the skull base. It enables the surgeon to look around blind corners and work behind structures that are hidden from microscopic view.     

Microsurgical Localization of the Cochlea in the Extended Middle Fossa Approach

Objective In the extended middle fossa approach, a portion of the petrous bone known as Kawase''s rhomboid can be drilled to expose the posterior fossa through a middle fossa corridor. During this bony resection, the cochlea is placed at risk. The objective of this study was to objectively detail the position of the cochlea in relation to reliable surgical landmarks.Methods Eleven cadaveric specimens were dissected—including six cadaveric heads and five dry temporal bones by means of an anterior petrosectomy with skeletonization of the cochlea. Three anatomic measurements describing the location of the cochlea in relation to the extrapolated intersection of the greater superficial petrosal nerve (GSPN) and facial nerve were recorded. These measurements were then correlated with thin-cut temporal bone computed tomography scans from 25 patients with morphologically normal inner ears.Results In the cadaveric specimens, the anterior border of the membranous basal turn of the cochlea was located an average of 7.56 mm (6.4 to 8.9 mm) anterior to the extrapolated junction of the GSPN and facial nerve, as measured along the course of the GSPN. The medial border of the membranous cochlea (medial margin of basal turn) was located an average of 8.2 mm (6.9 to 8.9 mm) medial to the extrapolated junction of the GSPN and facial nerve, as measured along the course of the facial nerve. The average maximum distance from the extrapolated junction of the GSPN and facial nerve to the membranous cochlea was 9.3 mm (8.2 to 10.3 mm). These anatomic measurements correlated well with radiologic measurements of the same parameters.Conclusion When drilling Kawase''s rhomboid, it is useful to locate the extrapolated junction of the GSPN and the facial nerve. Drilling of the anteromedial petrous bone outside of a radius of 12.5 mm from the extrapolated junction of GSPN and facial nerve appears to be associated with a low degree of risk to the cochlear apparatus.     

Transethmoidal approach to the optic canal: surgical and radiological microanatomy

BACKGROUND: The purpose of the study is to describe anatomic topographic landmarks for transethmoidal approach to optic canal for optic nerve decompression. The study focuses on microsurgical/radiologic anatomies and their relationships in the region of the optic canal and orbit. METHODS: Human optic canal and related anatomic structures were studied in orbits of 6 formalin preserved adult human cadavers. In addition, anatomic measurements were made with digital vernier caliper on the orbits of 25 adult human skulls. The relation between ethmoidal and sinus was assessed with computed tomography (CT) scan in 25 living human heads needing cranial CT scan for any reason. RESULTS: The suture on the conjunction of frontal, maxilla, and lacrimal bones with a location in medial side of the orbit was accepted as a landmark. When the measurements were taken from this landmark, the distances to supraorbital margin were: right(R): 16.76 +/- 2.62 mm, left (L): 17.10 +/- 1.97 mm, and to infraorbital margin were R: 20.18 +/- 3.24 mm, L: 18.94 +/- 2.19 mm. The distances to the anterior ethmoidal foramen were R: 19.66 +/- 3.96 mm, L: 19.11 +/- 2.84 mm, and to the posterior ethmoidal foramen were R: 32.01 +/- 2.90 mm, L: 32.62 +/- 3.33 mm. Mean distance between the anterior and posterior ethmoidal foramen were R: 12.55 +/- 3.4 mm, L: 13.51 +/- 4.2 mm. The posterior ethmoidal foramen and optic ring were separated only by the mean distances of R: 5.34 +/- 2.81 mm, L: 4.9 +/- 3.35 mm. The distance from the suture to the distal (orbital) opening of the optic canal was R: 37.35 +/- 2.73 mm, L: 37.52 +/- 3.47 mm and to proximal (intracranial) opening of the canal were R: 49.52 +/- 2.62 mm, L: 50.94 +/- 3.35 mm. The average widths of proximal (intracranial) canal measured were R: 7.43 +/- 1.95 mm, L: 7.38 +/- 2.01 mm and those of distal canal (orbital) were R: 5.12 +/- 1.1 mm, L: 4.95 +/- 1.32 mm. The mean lengths of the optic canal were R: 11.19 +/- 2.68 mm, L: 12.42 +/- 3.38 mm. In radiologic examinations, the mean numbers of anterior group ethmoidal cells were R: 7, L: 6 and those of posterior group ethmoidal cells were R: 4, L: 3. The results of CT demonstrated 7 (14%) Onodi or sphenoethmoidal cells in 50 orbits of living humans. CONCLUSION: The examination of radiologic anatomy in addition to microanatomy can significantly contribute to preoperative and postoperative evaluation of the patients.     

Anatomy of the Inferior Orbital Fissure: Implications for Endoscopic Cranial Base Surgery

Considering many approaches to the skull base confront the inferior orbital fissure (IOF) or sphenomaxillary fissure, the authors examine this anatomy as an important endoscopic surgical landmark. In morphometric analyses of 50 adult human dry skulls from both sexes, we divided the length of the IOF into three segments (anterolateral, middle, posteromedial). Hemotoxylin- and eosin-stained sections were analyzed. Dissections were performed using transnasal endoscopy in four formalin-fixed cadaveric cranial specimens (eight sides); three endoscopic approaches to the IOF were performed. IOF length ranged from 25 to 35 mm (mean 29 mm). Length/width of the individual anterolateral, middle, and posteromedial segments averaged 6.46/5, 4.95/3.2, and 17.6/ 2.4 mm, respectively. Smooth muscle within the IOF had a consistent relationship with several important anatomical landmarks. The maxillary antrostomy, total ethmoidectomy approach allowed access to the posteromedial segment of the fissure. The endoscopic modified, medial maxillectomy approach allowed access to the middle and posterior-medial segment. The Caldwell-Luc approach allowed complete exposure of the IOF. The IOF serves as an important anatomic landmark during endonasal endoscopic approaches to the skull base and orbit. Each of the three segments provides a characteristic endoscopic corridor, unique to the orbit and different fossas surrounding the fissure.     

Anatomo-Radiological Evaluation of Lateral Approaches to the Skull Base

Our objective is to correlate the anatomical exposure provided by complex skull base approaches to the lateral skull base with their CT and MRI scans counterparts and to introduce a modular concept emphasizing the derivation of complex skull base approaches from simpler ones.

We executed 10 lateral approaches to the skull base in 20 embalmed cadaveric heads (40 sides). Each approach was executed a minimum of three times on each specimen. These approaches were the pterional and its modifications, the subtemporal and its modifications, and the suboccipital and its modifications. We correlated the approaches and the areas of the skull base exposed by scanning the surgical cavity filled with material imageable by CT and MRI and throughly surveying the operative field.

Visualization of the area of the skull base exposed was excellent using our CT-MRI imageable cadaveric preparation. The topographic areas of the skull base exposed correlated well with their radiological counterparts.

The areas of the skull base exposed by each of the complex surgical approaches to the skull base were clearly delineated by using our anatomo-radiological correlation. Complex approaches to the skull base are formed by simple neurosurgical approaches (building blocks) to which different modules are added.

     

窦三角区的显微解剖学研究

目的　探讨窦三角区内各结构的形态和毗邻关系 ,以指导扩大的乙状窦前手术入路的手术操作。　方法　在手术显微镜下 ,对 10具尸体头颅标本按扩大的乙状窦前入路进行解剖 ;对 15个颅底窦三角区进行解剖观测 ;对 4个尸体头颅切片 ,制成 0 5～ 1 0mm超薄断层切片 ,对有关结构进行观测。　结果　静脉球可分为高位型、正常型和低位型。高位型出现率 ,左、右侧分别为 8%和18% ,两侧差异有非常显著性意义 (P <0 0 1) ;正常型出现率 ,左、右侧分别为 3 6%和 3 0 % ;低位型出现率左、右侧分别为 6%和 2 %。后半规管至岩部后表面水平距离为 ( 4 1± 1 1)mm。面神经管垂直段至颈静脉球间的距离 ,左、右侧分别为 ( 3 2± 0 5 )mm和 ( 2 0± 0 4 )mm。颈静脉球至内耳门后缘距离 ,左、右侧分别为 ( 7 5± 1 7)mm和 ( 4 0± 1 0 )mm。　结论　掌握窦三角区内各结构的形态和毗邻关系 ,有助于指导扩大的乙状窦前入路手术 ,预防重要结构的损伤     

Modified Subtotal Lothrop Procedure for Extended Frontal Sinus and Anterior Skull Base Access: A Cadaveric Feasibility Study with Clinical Correlates

Objective The endoscopic modified Lothrop procedure (EMLP) is an established approach for recalcitrant frontal sinus disease and anterior skull base exposure. However, in select cases, this technique may involve unnecessary resection of sinonasal structures. In this study, we propose a modification of the EMLP, termed the modified subtotal-Lothrop procedure (MSLP), to access the anterior skull base and complex frontal sinus disease for which access to the bilateral frontal sinus posterior table is required.Methods A cadaveric dissection with photo documentation was performed at an academic medical center on four cadaver heads using standard endoscopic techniques to demonstrate the MSLP and its feasibility.Results The endoscopic MSLP allowed ample access for instrumentation in each of the dissections using a 30- or 70-degree endoscope. Adequate bilateral access to the posterior table of the frontal sinus was gained in all cases without the need for dissection of the contralateral frontal sinus recess (FSR).Conclusion The MSLP appears to be a feasible technique for exposure of the anterior skull base and accessing complex frontal sinus pathology. This modification provides similar anterior skull base exposure and surgical maneuverability as the EMLP while limiting surgical dissection to one FSR, thereby preserving as much of the natural mucociliary drainage pathways as possible.